U.S. patent application number 10/384604 was filed with the patent office on 2003-09-18 for packet transmission system, packet transmission method, packet transmission device, home agent, mobile terminal, and access router.
This patent application is currently assigned to NTT DoCoMo, Inc.. Invention is credited to Kawai, Hiroyuki, Okajima, Ichiro, Umeda, Narumi.
Application Number | 20030174733 10/384604 |
Document ID | / |
Family ID | 27764515 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030174733 |
Kind Code |
A1 |
Kawai, Hiroyuki ; et
al. |
September 18, 2003 |
Packet transmission system, packet transmission method, packet
transmission device, home agent, mobile terminal, and access
router
Abstract
A packet transmission system is provided to achieve a higher
throughput in downlink packet transmission to a mobile node. When
there is a packet call directed to the mobile node, a transmission
node in a network in this packet transmission system retrieves
information as to a connection point of the mobile node from a
distribution location information holder of a home agent. Packets
are inputted to a packet distributor situated at the logical
location designated by the retrieved connection point information.
The packets are then distributed by the packet distributor to radio
transmission devices, and are transmitted at once.
Inventors: |
Kawai, Hiroyuki;
(Yokosuka-shi, JP) ; Okajima, Ichiro;
(Yokohama-shi, JP) ; Umeda, Narumi; (Yokohama-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
NTT DoCoMo, Inc.
Tokyo
JP
|
Family ID: |
27764515 |
Appl. No.: |
10/384604 |
Filed: |
March 11, 2003 |
Current U.S.
Class: |
370/498 ;
370/338 |
Current CPC
Class: |
H04W 8/04 20130101; H04W
28/06 20130101; H04L 45/00 20130101; H04W 40/12 20130101; H04W
80/04 20130101; H04W 40/30 20130101; H04L 69/14 20130101; H04W
40/08 20130101; H04W 88/14 20130101; H04L 45/24 20130101; H04W
40/36 20130101 |
Class at
Publication: |
370/498 ;
370/338 |
International
Class: |
H04J 003/00; H04Q
007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2002 |
JP |
2002-069000 |
Claims
What is claimed is:
1. A packet transmission system comprising: a mobile node; a
network that has a radio link with the mobile node, and transmits
downlink packets to the mobile node; and a home agent that manages
connection point information about the mobile node in the network,
the network including a packet distributor that inputs and divides
packets to be transmitted to the mobile node, and a packet parallel
transmitter that distributes the packets divided by the packet
distributor to a plurality of radio transmission devices provided
in advance and transmits the packets through the radio transmission
devices at once, the mobile node including a packet receiver that
receives the packets transmitted by the packet parallel transmitter
with a plurality of radio reception devices, and a packet combiner
that combines the received packets to generate an original packet
stream, the home agent including a distributor location information
holder that holds information of a logical location of the packet
distributor as information of a connection point of the mobile node
in the network, and when the network has packets to be transmitted
to the mobile node, the network retrieving the connection point
information from the distributor location information holder of the
home agent, and inputting the packets to the packet distributor
situated at the logical location specified by the retrieved
connection point information.
2. The packet transmission system as claimed in claim 1, wherein
the packet distributor includes a communicable radio transmitter
detector that determines whether each of the radio transmission
devices is communicable with the mobile node.
3. The packet transmission system as claimed in claim 1, wherein
the packet distributor includes a packet distribution ratio setting
part that sets an equal distribution ratio or a predetermined
distribution ratio with which the packets to be transmitted are
distributed.
4. The packet transmission system as claimed in claim 1, wherein
the packet distributor changes the distribution ratio with which
the packets to be transmitted are distributed, based on the
reported information sent by the reported information notifying
part.
5. The packet transmission system as claimed in claim 1, wherein:
the packet distributor includes a packet transfer part that
transfers the packets distributed to the radio transmitters to the
packet combiner in accordance with lower-layer protocols; and the
packet combiner includes a packet retriever that retrieves packets
transferred by the packet transfer part in accordance with the
lower-layer protocols.
6. The packet transmission system as claimed in claim 1, further
comprising a router that relays packets from the network to the
radio transmission devices, wherein the distributor location
information holder of the home agent is provided in the router.
7. A method of transmitting downlink packets from a network to a
mobile node, with the network being connected to a home agent that
manages information as to a connection point of the mobile node
located in the network, and the network including a distribution
node that inputs and distributes packets, the method comprising the
steps of: retrieving information as to a logical location of the
distribution node as the connection point information held in the
home agent, when transmitting the packets to the mobile node;
inputting the packets to the distribution node situated at the
logical location designated by the retrieved connection point
information; transmitting the distributed packets from the
distribution node to the mobile node through a plurality of radio
transmission devices that are set in advance; and combining the
packets transmitted through the radio transmission devices so as to
generate an original packet stream by the mobile node.
8. A packet transmission device that is connected to a network
including a transmission node and a plurality of radio transmission
devices, and transmits packets directed to a mobile node via the
network, the packet transmission device comprising: a packet
distributor that distributes packets from the transmission node to
the radio transmission devices; and a communicable radio
transmitter detector that determines whether each of the radio
transmission devices to which packets are distributed can
communicate with the mobile node.
9. The packet transmission device as claimed in claim 8, wherein
the packet distributor includes a packet distribution ratio setting
part that sets an equal distribution ratio or a predetermined
distribution ratio with which the packets to be transmitted are
distributed.
10. The packet transmission device as claimed in claim 8, wherein
the packet distributor changes the packet distribution ratio with
which the packets to be transmitted are distributed, based on
reported information supplied from each of the radio transmission
devices.
11. The packet transmission device as claimed in claim 8, wherein
the packet distributor includes a packet transfer part that
transfers the packets distributed to the radio transmission devices
to a packet combiner in accordance with lower-layer protocols.
12. The packet transmission device as claimed in claim 11, wherein
the packet distributor includes a special-purpose packet transfer
(link) part that transfers the packets distributed to the radio
transmission devices through a special-purpose link.
13. The packet transmission device as claimed in claim 12, wherein
the packet distributor includes a packet upper-layer transfer part
that transfers the packets distributed to the radio transmission
devices in accordance with the upper-layer protocols.
14. A home agent that manages information of connection points of a
mobile node in a network that includes a distribution node for
inputting and distributing packets, the home agent comprising a
distributor location information holder that holds information of a
logical location of the distribution node as the connection point
information.
15. The home agent as claimed in claim 14, further comprising a
tunneling part that encapsulates a packet with another header and
inputs the packet to the distribution node, when there is a packet
call directed to the mobile node.
16. The home agent system as claimed in claim 14, wherein the
distributor location information holder includes a distribution
node registration/update part that registers logical location
information of another packet distributor determined by a distance
between the mobile node and a radio transmission device to which
packets are to be transmitted from the packet distributor being
currently used by the mobile node when the mobile node moves a
certain distance away from the radio transmission device, the other
packet distributor being thereby registered as a new packet
distributor to be used by the mobile node.
17. The home agent system as claimed in claim 14, wherein the
distribution node registration/update part updates and re-registers
the logical location information of the packet distributor based on
information supplied from the mobile node.
18. A mobile terminal that receives downlink transmission packets
from a network that includes a distribution node for inputting and
distributing packets to be transmitted to the mobile terminal, the
mobile terminal comprising a packet combiner that receives packets
distributed by the distribution node and transmitted from a
predetermined radio transmitter to a predetermined radio receiver,
and combines the received packets, the predetermined radio receiver
being provided in the packet combiner.
19. The mobile terminal as claimed in claim 18, further comprising
a communication possibility notifying part that determines whether
the mobile terminal can communicate with a plurality of radio
transmission devices, and notifies the distribution node of the
determination result.
20. An access router that relays packets transmitted from a
transmission node in a network to a mobile node, the network
including a distribution node that inputs and distributes packets
to be transmitted to the mobile node, the access router comprising
a reported information notifying part that sends the distribution
node at least one item of information as reported information
selected from information items including information as to each
communicable band area, information as to communication charges,
information as to a delay in packet transfer from the packet
distributor to the one or more radio transmitters, and information
as to communication quality.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to packet
transmission systems and packet transmission methods, and, more
particularly, to a packet transmission system and a packet
transmission method that perform downlink packet transmission from
a network to a mobile node. The present invention also relates to a
packet transmission device, a home agent, a mobile terminal, and an
access router, all of which are employed in the packet transmission
system. The present invention is aimed at increasing throughput of
transmission packets.
[0002] As the IP (Internet Protocols)-based services have
dramatically increased in recent years, mobile communication
systems having higher affinities for IP traffic have been
developed. In an IP-based mobile communication system (hereinafter
referred to simply as the "packet transmission system"), packets
directed to a mobile node (such as a portable telephone device) are
transmitted through an access router (a router equipped with
devices such as radio transmitters that can perform radio
communication with the mobile node) that is situated at such a
location as to be communicable with the mobile node.
[0003] For instance, when the mobile node moves to an end of an
area within which the access router can perform transmission (this
type of area will be hereinafter referred to simply as a "cell"),
the transmission by the single access router becomes intermittent,
resulting in quality degradation. To avoid quality degradation in
the conventional packet transmission system, the cells are slightly
overlaid on one another, so that a plurality of neighboring access
routers can perform transmission to the mobile node when the mobile
node exists in the vicinity of a cell edge. A handover technique is
also applied to the above method so as to attenuate the quality
degradation. Handover techniques can be divided into hard handover
techniques and soft handover techniques. In a hard handover
technique, an access router that can perform the best communication
with the mobile node at a certain time is selected, and
communication is performed with the mobile node through the
selected access router. In a soft handover technique, on the other
hand, a plurality of access routers that can perform transmission
to the mobile node are selected, and the identical packets are
transmitted to the mobile node through the selected access routers
at the same time.
[0004] A conventional mobile node can be equipped with a plurality
of radio receivers, and can switch the radio receivers according to
a radio access method (such as the TDMA method or the CDMA method)
that can be used in the area in which the mobile node is located.
With the radio multiple receivers, the mobile node has the
advantage of being able to perform communication as long as one of
the radio receivers is communicable.
[0005] In the above conventional packet transmission system,
however, the mobile node can receive only one packet at a time,
regardless of which handover technique is employed. Accordingly,
only one packet is transmitted to the mobile node, even where the
access routers can perform packet transmission with high quality.
As a result, the throughput in the conventional packet transmission
system is always low.
[0006] Also, in the conventional packet transmission system, even
when the mobile node employs a plurality of radio access methods
and therefore more than one radio access methods are available,
only one of the radio access methods is selected for transmission
at a time, also resulting in a low throughput.
SUMMARY OF THE INVENTION
[0007] A general object of the present invention is to provide
packet transmission systems and packet transmission methods in
which the above disadvantages are eliminated.
[0008] A more specific object of the present invention is to
provide a packet transmission system and a packet transmission
method by which throughput in downlink packet transmission to a
mobile node can be increased.
[0009] Another specific object of the present invention is to
provide a packet transmission device, a home agent, a mobile
terminal, and an access router that are employed in the packet
transmission system of the present invention.
[0010] The above objects of the present invention are achieved by a
packet transmission system that includes: a mobile node; a network
that has a radio link with the mobile node, and transmits downlink
packets to the mobile node; and a home agent that manages
connection point information about the mobile node in the network.
In this packet transmission system, the network includes a packet
distributor that inputs and divides packets to be transmitted to
the mobile node, and a packet parallel transmitter that distributes
the packets divided by the packet distributor to a plurality of
radio transmission devices provided in advance and then transmits
the packets through the radio transmission devices. The mobile node
includes a packet receiver that receives the packets transmitted by
the packet parallel transmitter with a plurality of radio reception
devices, and a packet combiner that combines the received packets
to generate an original packet stream. The home agent includes a
distributor location information holder that holds information of a
logical location of the packet distributor as information of a
connection point of the mobile node in the network. In this packet
transmission system, when the network has packets to be transmitted
to the mobile node, the network retrieves the connection point
information from the distributor location information holder of the
home agent, and inputs the packets to the packet distributor
situated at the logical location specified by the retrieved
connection point information.
[0011] In this packet transmission system, packets to be
transmitted are distributed to the radio transmission devices by a
distribution node, and are then transmitted to the mobile node
through each of the radio transmission devices at once. Each of the
packets is received by the radio reception devices in the mobile
node. The packets are then combined to generate the original packet
stream. Thus, the throughput of downlink packets transmitted from
the network can be increased.
[0012] In the above packet transmission system, the radio
transmission devices may be formed by one or more access routers
each including one or more radio transmitters.
[0013] Also, in the above packet transmission system, the packet
distributor may be provided within the one or more access
routers.
[0014] In this packet transmission system, the distribution node is
provided in the vicinity of the access routers, so that the group
of radio receivers that can receive packets is reported directly to
the distribution node from the mobile node. Thus, more precise
packet transmission can be performed.
[0015] In the above packet transmission system, the packet
distributor may include a communicable radio transmitter detector
that determines whether each of the radio transmission devices is
communicable with the mobile node.
[0016] In this packet transmission system, the distribution node
inquires of each of the radio transmission devices that can serve
as packet destinations whether it exists within an area in which
the radio reception devices of the mobile node can perform
communication. The distribution node then selects each radio
transmission device that exists within the communicable area. Thus,
more precise downlink packet transmission can be performed.
[0017] As the mobile node can decide whether downlink communication
can be performed, the mobile node in the above packet transmission
system may include a communication possibility notifying part that
determines whether the mobile node can communicate with the radio
transmission devices, and notifies a distribution node provided
with the packet distributor of the determination result.
[0018] In the above packet transmission system, the packet
distributor may include a packet distribution ratio setting part
that sets an equal distribution ratio or a predetermined
distribution ratio with which packets to be transmitted are
distributed.
[0019] In this packet transmission system, packets are distributed
at the same distribution rate, and the control process for packet
distribution can be simplified, as long as the band widths of the
radio transmission paths are substantially uniform.
[0020] To determine the packet distribution ratio in accordance
with the conditions for communication or the requirements in the
system, each of the access routers in the above packet transmission
system may include a reported information notifying part that sends
the packet distributor at least one piece of information as
reported information, previously selected from information pieces
including information as to each communicable band area,
information as to communication charges, information as to delays
in packet transfer from the packet distributor to the one or more
radio transmitters, and information as to communication
quality.
[0021] Also, in the above packet transmission system, the packet
distributor may change the distribution ratio with which packets to
be transmitted are distributed, based on the reported information
sent by the reported information notifying part.
[0022] In this packet transmission system, packet distribution can
be performed based on the specification and quality of each radio
transmission path, using the information as to each communicable
band area. Accordingly, packet transmission can be performed
according to a distribution ratio that reflects the performance and
the congestion state of each radio transmission path.
[0023] When the charges for the radio transmission paths vary, the
communication charge information is used to perform highly
economical packet transmission for users.
[0024] Using the information as to the delay in packet transfer
from the distribution node to the access routers, packet transfer
priority can be given to radio transmitters having smaller transfer
delays. Thus, the packet transfer delay between the distribution
node and the combiner in the mobile node can be minimized.
[0025] Using the information as to quality of service (QoS), packet
transmission can be performed with quality corresponding to the
quality of service.
[0026] Also, in the packet transmission system of the present
invention, the packet distributor may include a packet transfer
part that transfers packets distributed to the radio transmitters
to the packet combiner in accordance with upper-layer protocols.
The packet combiner may include a packet retriever that retrieves
packets transferred by the packet transfer part in accordance with
the upper-layer protocols.
[0027] In this packet transmission system, packet distribution and
packet combining can be carried out in a lower layer, and,
accordingly, the process delay caused by those processes can be
minimized. Also, in this structure, the process of registering the
logical location information of the distribution node that is the
connection point of the upper layer, and the control operation of
changing distribution ratios with a local move of the mobile node,
are all performed in the lower layer. Accordingly, local handovers
can be hidden from the upper layer. Thus, the delay in handover
processes can be minimized, even if the home agent is situated at a
distance from the distribution node (at a location where a greater
process delay is caused in control data transfer in both
directions). Further, if the load on the home agent becomes large
due to similar handover process requests from a plurality of
distribution nodes, the total load can be reduced.
[0028] Also, in the packet transmission system of the present
invention, the packet distributor may include a special-purpose
packet transfer (link) part that transfers packets to be
distributed to the radio transmission devices through a
special-purpose communication path.
[0029] In this packet transmission system, a part of or all of the
transfer from the distribution node to the radio transmission
devices is performed through the special-purpose communication
path, instead of the upper layer. Thus, the packet transfer delay
can be minimized.
[0030] Also, in the packet transmission system of the present
invention, the packet distributor may include a packet upper-layer
transfer part that transfers packets to be distributed to the radio
transmission devices in accordance with upper-layer protocols.
[0031] In this packet transmission system, a part of or all of the
transfer from the distribution node to the radio transmission
devices is performed using the transfer function of the upper
layer. Accordingly, packets can be distributed to desired radio
transmission devices, as long as the connectability of the upper
layer is maintained. Thus, the throughput can be increased.
[0032] Also, in the above packet transmission system of the present
invention, the distributor location information holder may include
a distribution node registration/update part that registers logical
location information of another packet distributor determined by a
distance between the mobile node and a radio transmission device to
which packets are to be transmitted from a packet distributor being
currently used by the mobile node when the mobile node moves a
certain distance away from the radio transmission device, the other
packet distributor being thereby registered as a new packet
distributor to be used by the mobile node.
[0033] In this packet transmission system, the frequency of update
of the logical location information of the distribution node (i.e.,
the connection point information of the upper layer) to be
registered in the distributor location information holder of the
home agent is made sufficiently lower than the switching frequency
of the access routers that mainly perform packet transmission to
the mobile node, so that the handover frequency in the upper layer
can be lowered. As a result, the process necessary for the
upper-layer handover can be simplified, and handover can be carried
out at a higher speed.
[0034] In the above packet transmission system, the distribution
node registration/update part may update and re-register the
logical location information of the packet distributor based on
information supplied from the mobile node.
[0035] Also, in the above packet transmission system, the mobile
node may be a mobile communication terminal.
[0036] The above packet transmission system of the present
invention may further include a router that relays packets from the
network to the radio transmission devices. In this packet
transmission system, the distributor location information holder of
the home agent is provided in the router.
[0037] In this packet transmission system, the upper-layer
connection point information to be registered in the home agent is
held by the router. Thus, a simpler packet transmission system can
be realized.
[0038] The above objects of the present invention are also achieved
by a method of transmitting downlink packets from a network to a
mobile node, with the network being connected to a home agent that
manages information as to a connection point of the mobile node
located in the network. The network includes a distribution node
that inputs and distributes packets to be transmitted. This method
includes the steps of:
[0039] retrieving information as to a logical location of the
distribution node as the connection point information held in the
home agent, when transmitting packets to the mobile node;
[0040] inputting the packets to the distribution node situated at
the logical information designated by the retrieved connection
point information;
[0041] transmitting the distributed packets from the distribution
node to the mobile node through a plurality of radio transmission
devices that are set in advance; and
[0042] combining the packets transmitted through the radio
transmission devices so as to generate an original packet stream by
the mobile node.
[0043] The above and other objects and features of the present
invention will become more apparent from the following description
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 illustrates an example structure of a packet
transmission system in accordance with a first embodiment of the
present invention;
[0045] FIG. 2 illustrates an example of the arrangement of cells in
a cellular system;
[0046] FIG. 3 illustrates an example structure of the cellular
system shown in FIG. 2;
[0047] FIG. 4 illustrates another example structure of the cellular
system shown in FIG. 2;
[0048] FIG. 5 illustrates an example of the arrangement of cells in
an overlaid communication system in which a single cell system and
a cellular system are overlaid on each other; and
[0049] FIG. 6 illustrates an example structure of the overlaid
communication system shown in FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] The following is a description of embodiments of the present
invention, with reference to the accompanying drawings.
[0051] FIG. 1 illustrates an example structure of a packet
transmission system in accordance with a first embodiment of the
present invention. As shown in FIG. 1, the packet transmission
system of the present invention can be roughly divided into a
network 150 and a mobile node (a mobile terminal) 107 (indicated by
the dotted lines).
[0052] The network 150 includes a home agent 101 that holds the
connection point information of the upper layers (such as the
Internet protocols) of the mobile node 107 in the network 150, a
distribution node 102 that distributes transmission packets
directed to the mobile node 107, and radio transmission devices
103-1 through 103-M (M is an integer greater than 0) that provide
radio links for the mobile node 107. The radio transmission devices
103-1 through 103-M will be hereinafter referred to as the "access
routers". Each of the access routers 103-1 through 103-M is
provided with N.sub.1, N.sub.2, . . . , N.sub.M of radio
transmitters 104-1 through 104-.SIGMA..sub.Ni
(.SIGMA..sub.Ni=N.sub.1+N.sub.2+. . . +N.sub.M) , and the number M
of the access routers is 1 or greater. The number of radio
transmitters included in each of the access routers 103-1 through
103-M is also 1 or greater. The distribution node 102 may be
independently located in the network 150, or may be provided to an
arbitrary one(s) of the access routers 103-1 through 103-M. In this
example, the distribution node 102 is independently located in the
network 150. There may be two or more devices that function as the
distribution node 102, but only one device should function as the
distribution node for one mobile node.
[0053] The mobile node 107 includes one or more radio receivers
105-1 through 105-L that receive packets transmitted from the
access routers 103-1 through 103-M of the network 150, and a
combiner 106 that combines the received packets to generate a
packet stream. The number L of the radio receivers 105-1 through
105-L provided in the mobile node 107 can be determined from the
number of radio signals that are desired to be received. This
mobile node 107 may be a portable telephone terminal, a portable
information terminal equipped with the above radio receivers, or an
in-car terminal, for example. Each of the radio transmitters 104-1
. . . , 104-.SIGMA..sub.Ni in the network 150 is capable of
communicating with one or more of the radio receivers 105-1 through
105-L in the mobile node 107.
[0054] The operation principles of the present invention will now
be described, with reference to FIG. 1. Although not shown in the
drawing, this packet transmission system has a transmission node
for transmitting packets in the network 150. This transmission node
is provided with IPs (such as Internet protocols) as upper layers,
and performs packet transmission with a reception node (i.e., the
mobile node 107 in this case) in accordance with the IPs. In the
following, the operation in accordance with the above principles of
the present invention will be described.
[0055] (Operation Principles)
[0056] When packets are transmitted from the transmission node of
the network 150 to the mobile node 107, the transmission node
inquires of the home agent 101 to which one(s) of the access
routers 103-1 through 103-M in the network 150 should packets be
transferred so as to be transmitted to the mobile node 107 The
transmission node retrieves the information as to the logical
location of the distribution node 102 that distributes packets to
access routers suitable for transmitting packets to the mobile node
107, and transmits transmission packets to the distribution node
situated at the logical location. Receiving packets from the upper
layer of the transmission node, the distribution node 102
distributes the received packets to a part of or all of the radio
transmitters 104-1 . . . , 104-.SIGMA..sub.Ni included in the
access routers 103-1 through 103-M. The packets distributed to a
part of or all of the radio transmitters 104-1 . . . ,
104-.SIGMA..sub.Ni are then transmitted from these radio
transmitters to the mobile node 107 through radio transmission
paths.
[0057] After being received by the radio receivers 105-1 through
105-L of the mobile node 107, the packets transmitted from the
radio transmitters in the above manner are combined by the combiner
106 to generate the original packet stream, which is outputted to
the next step.
[0058] As described above, in the network 150, packets transmitted
through the upper layer of the transmission node are distributed to
one or more of the radio transmitters 104-1 . . . ,
104-.SIGMA..sub.Ni by the distribution node 102 (different packets
being distributed to each radio transmitter). These packets
transmitted through the radio transmission paths are received and
combined in the mobile node 107. Thus, a higher throughput can be
obtained. Also, the access routers equipped with radio transmitters
should be arranged in such a manner as to overlap one another. With
this arrangement, a greater number of access routers can perform
communication with the mobile node. Accordingly, the throughput in
the overlapping area is increased, and the packet transfer rate
with respect to the number of existing access routers can be
increased.
[0059] Next, a case where the above packet transmission system is
applied to an IP-based cellular system (hereinafter referred to
simply as the "cellular system"), and a handover operation is
performed in the cellular system will be described. In the
following, this case will be regarded as the first embodiment of
the present invention.
[0060] (First Embodiment)
[0061] FIG. 2 illustrates an example structure of the cells in the
cellular system. As can be seen from FIG. 2, the access routers
103-1 through 103-M are each arranged beforehand in each
corresponding one of cells 108-1 through 108-M. Each of the cells
108-1 through 108-M is wide enough for packet transmission through
each corresponding one of the access routers 103-1 through
103-M.
[0062] When existing within two or more cells, the mobile node 107
can receive packets transmitted from at least one of the access
routers 103-1 through 103-M. The end of each cell overlaps the end
of a neighboring cell, so that the service is not interrupted when
the mobile node 107 moves from one cell to another. Accordingly,
when located at the end of a cell, the mobile node 107 can usually
communicate with two or more access routers.
[0063] FIG. 3 illustrates an example system structure of the above
cellular system.
[0064] As shown in FIG. 3, this cellular system includes a network
109, a home agent 101, a transmission node 112, a router 110, the
access routers 103-1 through 103-M, and the mobile node 107. The
network 109 is connected to the home agent 101, the transmission
node 112 that transmits packets to the mobile node 107, and the
router (an edge router) 110 that relays packets transmitted from
the transmission node 112 to one or more designated access routers.
Each of the access routers 103-1 through 103-M in the network 109
is provided with the corresponding one of radio transmitters 104-1
through 104-M. The access method of these radio transmitters 104-1
through 104-M may be formed by a single method or combined methods,
as long as packets transmitted from the radio transmitters 104-1
through 104-M can be received by the mobile node 107. Each of the
access routers 103-1 through 103-M is provided with the
corresponding one of distribution nodes 102-1 through 102-M that
has a function of distributing packets. The access routers 103-1
through 103-M are arranged close to one another, and are connected
to one another via a local high-speed network 111. Also, the mobile
node 107 is provided with radio receivers 105-1 through 105-L that
receive packets transmitted from access routers via radio sections
and a combiner 106 that combines packets outputted from the radio
receivers 105-1 through 105-L.
[0065] In this embodiment, a local handover process (from the
distribution nodes to the combiner) is regarded as the protocols of
the link layer. The other general handover processes (such as the
process of the transmission node 112 transmitting packets to the
connection-point access router, referring to the home agent 101)
are contained in the network layer protocols such as mobile
IPs.
[0066] In the following, an operation of transmitting a downlink
packet from the transmission node 112 in the network 109 to the
mobile node 107 in the above structure will be described.
[0067] The mobile node 107 first determines which one(s) of the
radio transmitters 104-1 through 104-M in the network 109 can
communicate with the radio receivers 105-1 through 105-L of the
mobile node 107. This determination may be performed by the radio
receivers 105-1 through 105-L of the mobile node 107, which measure
the reception strengths of notification signals transmitted with a
known transmission power level from the radio transmitters 104-1
through 104-M of the network 109, then select only the radio
transmitters that have the reception strength levels above a
predetermined threshold level, and restrict the types and the
number of radio transmitters with which the mobile node 107 can
perform simultaneous packet reception. For instance, in a case
where the mobile node 107 only has the ability to receive signals
from three radio transmitters at once, the reception strengths of
notification signals are measured, and, even if the number of radio
transmitters that have the reception strength levels above the
predetermined threshold level is 4 or greater, the radio
transmitters having the three highest reception strength levels are
selected. Here, the predetermined threshold level may be
represented by either a predetermined electric power value or an
electric power value that varies with situations (for instance, a
value obtained by multiplying the reception strength value of the
radio transmitter having the highest radio strength by a
predetermined coefficient that is larger than 0 but smaller than
1).
[0068] The mobile node 107 next selects one of the radio
transmitters 104-1 through 104-M that has the transmission path in
an excellent condition and constantly performs excellent
transmission (the mobile node 107 selects the radio transmitter
104-1, for example). Although only one radio transmitter is
selected in this example for ease of explanation, it is possible to
select two or more radio transmitters in practice. The mobile node
107 requests the home agent 101 to register the logical location
information as to the distribution node (the distribution node
102-1 in this example) included in the access router that is the
selected radio transmitter, which constantly performs excellent
transmission. The mobile node 107 further makes the distribution
node 102-1 register the group of radio transmitters 104-1 through
104-M from which the mobile node 107 can receive packets.
[0069] When having transmission packets directed to the mobile node
107, the transmission node 112 inquires of the home agent 101
through which transmission path the packets should be transmitted
to the mobile node 107 in accordance with the IPs. As described
above, the home agent 101 has the logical location information of
the distribution node 102-1 registered as the address of the mobile
node 107. Accordingly, in response to the above inquiry from the
transmission node 112, the information indicating the logical
location of the "distribution node 102-1" is supplied. The
transmission node 112 then transfers the transmission packets to
the router 110, so that the packets reach the distribution node
102-1 selected in accordance with the home agent 101.
[0070] The packets, which have been subject to the routing by the
router 110 and have reached the distribution node 102-1, are
divided and distributed equally to the group of radio transmitters
104-1 through 104-M from which the mobile node 107 can receive
packets. This distribution is performed by the local high-speed
network 111, causing a slight delay in packet transfer. Although
the packet distributing method in this embodiment is an equal
distributing method, the distribution ratio of the packets may be
varied. In such a case, the distribution ratio of the packets is
varied based on one or more items of information including: {circle
over (1)} information as to each band area through which
communication with the mobile node 107 can be performed; {circle
over (2)} information as to communication charges; and {circle over
(3)} information as to a delay in packet transfer from the
distribution node to each corresponding radio transmitter.
[0071] For instance, if the band area through which communication
with one radio transmitter can be performed is wide ({circle over
(1)}), or if the charges for communication services provided
through the radio transmitter are low ({circle over (2)}) , or if
the delay in packet transfer from a distribution node 102-1 to the
radio transmitter is small ({circle over (3)}) , the distribution
node 102-1 increases the amount of packet distribution for the
radio transmitter. By doing so, the distribution node 102-1 can
perform more appropriate packet distribution based on the
information items ({circle over (1)}-{circle over (3)}) about each
of the radio transmitters 104-1 through 104-M, compared with a case
of equally dividing and distributing packets. The information as to
each communicable band area can be obtained by measuring the radio
transmitter or the mobile node measuring the condition of the
transmission path or the congestion state of the radio link. Also,
the information as to the communication charges can be obtained by
inquiring of the server that manages the charge information in the
network. A delay in packet transfer can be measured by dividing a
network delay in packet transfer to and from each of the radio
transmitters 104-1 through 104-M by 2.
[0072] The mobile node 107 monitors changes in the conditions (such
as reception conditions) of the group of radio transmitters from
which the mobile node 107 can receive packets in desired timing. If
there is a change detected, the mobile node 107 notifies the
distribution node 102-1 in the access router 103-1 of the result.
If the mobile node 107 moves far away from the access router 103-1,
some other distribution node can take over the distribution
function of the distribution node 102-1 serving the mobile node
107. More specifically, the mobile node 107 notifies the home agent
101 of the logical location information about the new distribution
node, and notifies the new distribution node of the group of radio
transmitters from which the mobile node 107 can receive packets.
This corresponds to a handover in the upper layers. However, there
is no need to immediately move the distribution function just
because radio transmitters that can perform the best transmission
are changed. Still, a better effect in minimizing the delay in data
transfer from the distribution node to each access router can be
expected by immediately moving the distribution function to a new
distribution node that is a handover destination. Also, the
distribution function can be moved, after the mobile node 107 moves
a certain distance away from the access router to which the
currently serving distribution node belongs (for instance, after
the radio transmitter in the access router to which the currently
serving distribution node belongs is removed from the list of
destinations of packet distribution performed by distribution
nodes). In this manner, the frequency of moving the distribution
function (i.e., the frequency of handover in the upper layers) can
be reduced, and the control operation involved in moving the
distribution function can be simplified. Accordingly, the frequency
of relaying the update information of the upper-layer connection
point of the mobile node 107 to the home agent 101 is reduced. Even
if the home agent 101 is located in a remote place, this packet
transmission method can prevent degradation in performance due to a
transmission delay between the home agent 101 and the upper-layer
connection point and an increase in traffic with a handover control
signal.
[0073] As a local handover is hidden from the upper layer, it is
not necessary to take the transitional conditions (such as soft
handover and buffering processes) of the handover into
consideration in designing the upper layer. Accordingly, the
handover protocols in the upper layer can be simplified. Further,
as the local high-speed network 111 is used for transferring local
packets, the transfer delay can be reduced, and packet transmission
with a smaller delay can be performed, compared with the packet
transfer by the upper layer.
[0074] If a radio access method or a radio reception structure in
which signals from the radio transmitters 104-1 through 104-M can
be received by one radio receiver is applied to the above
embodiment, only one radio receiver is sufficient for the mobile
node 107, as shown in FIG. 4. For instance, to realize this
structure, signals should be transmitted from the radio
transmitters 104-1 through 104-M in different timings (separately
from one another), and the radio receiver on the receiving end
should receive signals from each radio transmitter in timing
different from signals from the other radio transmitters. By
employing only one radio receiver in this manner, the throughput
can be increased without an increase of the number of radio
receivers in the mobile node 107.
[0075] In the following, an operation involving an overlaid system
with different types of networks will be described as a second
embodiment of the present invention.
[0076] (Second Embodiment)
[0077] FIG. 5 illustrates an example structure of an overlaid
system in which a single cell system (used in an in-house network
such as a wireless LAN) and a cellular system are overlaid on each
other. In FIG. 5, access routers 103-1 through 103-M are arranged
in cells 108-1 through 108-(M+1). Among these access routers 103-1
through 103-M, the access router 103-1 is equipped with radio
transmitters of two different types of radio access methods (such
as the CDMA method and the OFDM method), and therefore can transmit
packets to the different cells 108-1 and 108-2. The range at which
the access routers 103-1 through 103-M can transmit packets is
represented by the cells 108-1 through 108-(M+1). When existing in
more than one cell, the mobile node 107 can receive packets from
one of the corresponding access routers. The cells 108-2 through
108-(M+1) form a cellular system of a single radio access method.
As shown in FIG. 5, the communicable ranges at the cell edges of
each two neighboring cells overlap each other, so that the service
is not interrupted when the mobile node 107 moves from one cell to
another. Meanwhile, the cell 108-1 forms a single cell system. A
plurality of communication systems are overlaid in this manner, so
that communication can be performed with a plurality of access
routers not only at the cell edges but in the entire area of the
cells.
[0078] FIG. 6 shows an example structure of the system in which a
single cell system and a cellular system are combined as shown in
FIG. 5.
[0079] As can be seen from FIG. 6, this system includes a home
agent 101, a distribution node 102, access routers 103-1 through
103-M, a mobile node 107, a network 109, routers 110-1 through
110-N, and a transmission node 112. The network 109 is connected to
the home agent 101, the transmission node 112 that performs packet
transmission, and the routers (edge routers) 110-1 through 110-N
that relay packets from the transmission node 112 to the access
routers 103-1 through 103-M. Each of the routers 110-1 through
110-N is connected to the access routers 103-1 through 103-M.
Although each of the access routers 103-1 through 103-M is provided
with N types of radio transmitters in the drawing, it is not
necessary to employ all the N types of radio transmitters in
practice. The mobile node 107 is provided with one or more radio
receivers to receive signals transmitted from the radio
transmitters of the access routers 103-1 through 103-M, and a
combiner 106 that combines the packets received at the radio
receivers.
[0080] Although in FIG. 6 the total number (MN) of radio
transmitters provided in the access routers is the same as the
number (MN) of radio receivers provided in the mobile node 107,
these numbers may be different. The number of radio transmitters
and the number of radio receivers required can be arbitrarily
determined by the number of signals desired to be received
simultaneously at the mobile node 107 in accordance with the radio
access method.
[0081] In this embodiment, the distribution node 102 is
independently connected to the network 109, instead of being
connected directly to the insides of the access routers.
Accordingly, the distribution node 102 is connected to the radio
transmitters 104-1 through 104-(MN) in the access routers 103-1
through 103-M via the routers 110-1 through 110-N.
[0082] The transmission node 112 retrieves the logical location
information of the distribution node (the distribution node 102 in
this embodiment) to be used by the mobile node 107, i.e., the
connection point information as to the upper layer in the network
109, from the home agent 101. The transmission node 112 then
transmits packets to the upper-layer connection point (i.e., the
distribution node 102). The distribution node 102 distributes the
packets to the radio transmitters 104-1 through 104-(MN). At this
point, the distribution node 102 transfers the packets via the
routers 110-1 through 110-N, using the upper-layer protocols (the
Internet protocols, for instance), unlike the distribution node(s)
in the first embodiment. With the use of the upper-layer protocols
in the packet transfer, a greater delay in packet transfer is
expected, compared with a case where a special-purpose network is
employed. However, the advantages of the use of the upper-layer
protocols are that it is not necessary to employ a special-purpose
network to connect the radio transmitters, and that radio
transmitters to distribute and transmit packets can be selected
with greater flexibility. Accordingly, this embodiment can be
easily applied to packet transmission for application that does not
have very specific requirements for packet transmission delays
(such as text data transmission), so as to achieve a higher
throughput.
[0083] Also, in the packet transmission process for application
that has very specific requirements for packet transmission delays
(such as video image transmission in a TV conference), this
embodiment can be applied if the connection between the network and
the routers and the connection between the routers and the radio
transmitters are designed in such a manner that the transfer delay
due to packet transfer can be made small enough by comparing the
delay requirements using the upper layer. In this manner, a higher
throughput can be achieved.
[0084] A part of or all of the radio transmitters 104-1 through
104-(MN) can be interconnected to one another, if necessary, by a
local high-speed network in the same manner as in the first
embodiment. With the interconnection of a part of or all of the
radio transmitters 104-1 through 104-(MN) by a local high-speed
network, an increase of the transmission delay in this embodiment
can be restricted.
[0085] Although the home agent 101 holds the connection point
information of the upper layer in the first and second embodiments,
the present invention is not limited to this structure. For
instance, it is possible to employ a structure in which the routers
110 and 110-1 through 110-N hold the connection point information.
In such a case, the transmission node 112 retrieves the connection
point information from the router 110 or the routers 110-1 through
110-N so as to transmit packets to access routers that are
designated packet destinations.
[0086] Also, downlink packet transmission is performed only for one
mobile node in the first and second embodiments. However, the
present invention can be applied to multi-hop communication, if a
plurality of mobile nodes located in the vicinity of one another
are regarded as one virtual mobile node. In such a case, packets
are distributed to any one of the mobile nodes, and the mobile node
that has received the packets performs communication with the other
mobile nodes so as to transfer the packets to the other mobile
nodes. Accordingly, packet reception by all the mobile nodes via a
network is not necessary. Thus, the network resource can be more
efficiently utilized.
[0087] In the above embodiments, the distribution node 102 and the
distribution nodes 102-1 through 102-M correspond to the packet
distributor in the claims. The packet combining function of the
combiner 106 of the mobile node 107 corresponds to the packet
combiner and the packet retriever. The downlink quality
determination notifying function of the mobile node 107 corresponds
to the communication possibility notifying part. The connection
point information holding function of the home agent 101
corresponds to the distributor location information holder and the
distribution node registration/update part. The radio transmitting
function of each of the access routers 103-1 through 103-M
corresponds to the packet parallel transmitter. The receiving
function of each of the radio receivers 105, 105-1 through 105-L,
and 105-1 through 105-(MN) of the mobile node 107 corresponds to
the packet receiver. Further, the controlling function of each of
the distribution nodes 102 and 102-1 through 102-M corresponds to
the communicable radio transmitter detector. The packet
distribution controlling function of each of the distribution nodes
102 and 102-1 through 102-M corresponds to the packet distribution
ratio setting part and the packet transfer part. The communicating
function of each of the distribution nodes 102 and 102-1 through
102M corresponds to the special-purpose packet transfer (link) part
and the packet upper-layer transfer part. Further, the system
information notifying function of each of the access routers 103-1
through 103-M corresponds to the reported information notifying
part. The information holding and controlling function of each of
the routers 110 and 110-1 through 110-N corresponds to the
distribution location information holder.
[0088] It should be noted that the present invention is not limited
to the embodiments specifically disclosed above, but other
variations and modifications may be made without departing from the
scope of the present invention.
* * * * *